Seals of this type are generally known. In this case the fastening element is formed for example by a screw and the washer is formed by a so-called Usit ring. Usit rings are flat metallic rings having trapezoidal sealing beads, which are used for sealing screw connections and flanged joints. Usit rings are therefore self-sealing washers.
Two different types of Usit rings are known. In one type, the sealing bead is on the inside, whereas in the other type, it is on the outside.
When the fastening element is tightened, the flexible rubber sealing bead is elastically deformed until a metallic force locking effect is achieved via the flat ring.
Different material pairings are known for the flat ring of the Usit ring and for the sealing bead. Thus, for example, the flat ring can consist of a normal steel and the sealing bead can consist of an NBR or FKM material, subject to the temperatures which prevail. NBR materials are used for example when air and mineral oils are to be sealed at a temperature of up to 100° C. On the other hand, FKM materials are used for sealing air and mineral oils or synthetic oils at higher temperatures in each case. The previously known seals are not suitable for use in areas in contact with products in the food or pharmaceutical industries, nor are they suitable for use in plants in the food or pharmaceutical sectors because the previously known seals have many gaps and projections which are difficult to access and therefore also difficult to clean. Impurities in these regions can lead to contamination, which is unacceptable or not permissible in the food or pharmaceutical sectors.